An Investigation into the Approximations Used in Wave Packet Molecular Dynamics for the Study of Warm Dense Matter

Wave packet molecular dynamics (WPMD) is a computationally fast tool used to model warm dense matter systems [1]. WPMD is a non-adiabatic method that employs many approximations to achieve computational efficiency while implementing semi-empirical scaling parameters to retain accuracy. We investigate three of the main approximations in most variants of WPMD: a limited basis set, estimations of exchange, and dearth of correlation [2]. We examine each of these approximations through simulation of atomic and molecular hydrogen in addition to a dense hydrogen plasma. The most significant improvement to WPMD comes from combining a two-Gaussian basis with a semi-empirical correction based on the valence-bond wave function. A single parameter scales this correction to match the experimental pressures of dense hydrogen. The semi-empirical scaling parameters are necessary to correct the main approximations in WPMD. However, reducing the scaling parameters for more ab-initio terms gives more accurate results and displays the underlying physics more readily.

      1. R. A. Davis et al. Phys. Rev. Research. 2, 4 (2020).

      2. W. A. Angermeier and T. G. White, Plasma 4, 294 (2021).